The invention relates to a hydraulic telescopic shock absorber with a cylinder and with a piston which is displaceable therein and is retained by means of a piston rod which divides the cylinder into two chambers which are separated from one another by a piston. The two chambers are connected, or connectable, to one another via channels passing through, or bypassing, the piston or the piston rod. The channels are controllable, or adjustable at least partially, by an electromagnetic valve arrangement which is arranged on the piston rod and which controls a slide for varying the opening cross-section of the channels. The slide forms the armature, or a part, of an electromagnet connected thereto.
Shock absorbers of this general type are known according to German Patent Specification 2,911,768 or German Patent Specification 3,346,352. There a coil is arranged within a space communicating with one chamber or the other and is embedded in the hydraulic medium. Even though hydraulic media are usually produced on an oil base and therefore electrically insulating, such an arrangement presents problems because the hydraulic media contain more or less aggressive constituents which, under certain circumstances, can lead to corrosion or other damage on the coil and electrical lines.
The object of the invention is, therefore, to provide hydraulic telescopic shock absorbers in which the electrical components of the electromagnetic valves, serving for controlling the damping resistance, are accommodated in an especially operationally reliable manner.
According to the invention, this object is achieved because the coil(s) of the electromagnetic valve arrangement are accommodated in a housing which is sealed relative to the hydraulic medium and which is arranged on one side, for example the piston-rod side, of the piston. The coil, as seen in axial section through the telescopic shock absorber, is surrounded on its sides facing away from the armature in a U-shaped or C-shaped manner by ferromagnetic housing parts located on the same side as the armature and in a clearance between these housing parts, by non-magnetizable material. Apart from the fact that the coil is accommodated in a protected manner, this design guarantees good magnetic properties and correspondingly high adjusting forces, since the magnetic field surrounding the coil is guided and sharply focused through the ferromagnetic housing parts surrounding the coil and is accordingly effective at high field strengths in the transitional regions between these housing parts and the armature.
At the same time, the armature can be arranged in a space filled with hydraulic medium, so that without special sealing measures, the armature can be connected to the slide of the electromagnetic valve arrangement, or be provided as part of the slide valve.
To guarantee that the hydraulic forces acting on the armature are mutually compensated, or generate no appreciable force urging the armature in the direction of an end position, a first preferred embodiment of the invention provides that the coil housing surrounds a cylindrical space, which is open towards one chamber and in which the armature is arranged so as to be displaceable in a piston-like manner. The armature is made annular, or with an axial bore, so that there is an approximately equal hydraulic pressure on the two end faces of the armature.
In a further preferred embodiment, the armature is arranged on the end face of the coil. The receiving space for the coil in the housing is closed off on the same side as the armature by a plate made of non magnetizable material. At the same time, the armature is appropriately designed as a perforated circular disc, which is retained in one end position at a short distance from the plate by stop points arranged on the plate, or on the circular disc. This insures that the circular disc, or armature, is subjected to the pressure of the hydraulic medium on both sides in all possible positions. This design is characterized by a special simplicity in terms of construction, because the armature, or the circular disc, requires no guidance within the coil.
The electromagnetic valve arrangement is preferably controlled as a function of the pressure in at least one chamber, there appropriately being a differential-pressure measuring device which records the pressure difference between the two chambers. Since the pressure difference changes in proportion to the resistance offered by the shock absorber to the particular relative movement between the piston and cylinder, the pressure-difference signal emitted by the measuring device is also a measure of the particular supporting forces generated by the shock absorber. This type of control is therefore also especially suitable for those active suspension systems in which the supporting forces of the wheel support units are to be influenced directly.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.